An in-wheel motor system refers to a vehicle driving system having a motor positioned inside a wheel, the motor generating a driving force.
The in-wheel motor system includes an in-wheel motor, a cooling device to cool down the in-wheel motor, a decelerator to transmit a driving force to the wheel, a brake system to generate a braking force, a steering system to switch the direction of a vehicle, and a suspension system to support the wheel in the vehicle. In order to arrange the above-described parts in the wheel, connections between the parts are required to be integrated, and functions of the parts are required to be integrated.
In order to arrange an in-wheel motor generating a high-power driving force in the wheel, the size of the in-wheel motor is required to be reduced. In order to accomplish the size reduction, the structure of the in-wheel motor cooling device is important.
In the related art, there has been disclosed a structure which includes a mechanical oil pump and an oil tank provided inside an in-wheel motor system adjacent to a wheel driving shaft, in order to maximize the arrangement efficiency and cooling performance of the in-wheel motor system when the oil pump to circulate oil, the oil tank to store oil, an oil path through which oil circulates, and a discharge port to discharge oil are arranged to cool down the in-wheel motor.
In the in-wheel motor system according to the related art, the mechanical oil pump is located at the same position as the center of the wheel and disposed in the center of a counter gear to receive a motor driving force, in order to drive the oil pump through a rotational output of the in-wheel motor. The oil tank collecting oil is disposed over a suspension lower arm ball joint and under a decelerator so as to be located at a more inner position than a brake system in the vehicle.
In the in-wheel motor system according to the related art, a trochoid pump, a gear pump, or a vane pump which must be rotated by an external force so as to generate a discharge pressure is used as the mechanical oil pump to circulate oil. The mechanical oil pump has a problem in that the oil pump can circulate oil when the vehicle is moved forward, but cannot circulate oil when the vehicle is moved backward.
The oil discharge pressure is generated in proportion to the wheel speed. Therefore, when excessive heat is generated from the motor at a low speed (for example, when the vehicle travels on a climbing lane for a long time), the motor may not be efficiently cooled down.
Since the position of the oil tank storing oil is blocked by the surrounding parts, the oil tank cannot obtain a cooling effect by vehicle-induced wind.
The discussion in this section is only to provide background information of the invention disclosed in this application and does not constitute admission of prior art.